This proposal is concerned with the micromechanical properties of the sensory hair bundles. The author believes that most of our knowledge about hair bundle behavior is derived from stimuli that produce a static, low frequency or pulse displacement of the hairs. Data from these sources have advanced our understanding of hair micromechanics a great deal. However, the cochlear hair cell is designed to respond at high frequencies, and a physiology based on these stimuli may bias the picture of hair bundle and hair cell behavior. A microwaterjet has been developed which is capable of delivering a non-contact stimulus over a relatively wide bandwidth. Similarly, imaging technology, using stroboscopic illumination or photodiode detection has been developed, and this permits either direct visual observation of high frequency hair bundle motion, or examination of an electrical analogue of that motion. In vitro studies of hair cells on the chick basilar papilla are proposed in which hair bundle behavior is examined in relation to the stimulus waveshape, hair bundle stiffness, differential hair movements, and hair bundle resonance. In addition, the pathophysiology of hair behavior is studied following overstimulation. Hair bundle micromechanics are correlated with the receptor potential of the hair cell, and with the structural morphology of the bundle. Finally, new technological developments will be explored to improve and expand the measurement system. These include the development of reflected light microscopy to image inaccessible hair cells, the implementation of vital dye methods to study Ca++ flux in hair cells during stimulation, and isolated cochlear preparation for the gerbil, and micromechanical studies on isolated hair cells. The investigations presented in this proposal offer a new way of looking at hair cell micromechanics and I am confident that important observations, which expand our appreciation of the transduction process, will emerge.